#include<stdio.h>
#include<math.h>
int main()
{
    double x1, x2, y1, y2, d;
    while(scanf("%lf %lf %lf %lf", &x1, &y1, &x2, &y2) != EOF)
    {
        
        d = sqrt((x1-x2)*(x1-x2) + (y1-y2)*(y1-y2));
        printf("%.2f\n", d);
    }
    return 0;
}